JP3271123B2 - Method for producing composite of silicon nitride and boron nitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite of silicon nitride and boron nitride, and more particularly to a method of producing a composite of silicon nitride and boron nitride in which the resultant composite has improved thermal shock resistance. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, there is a composite material of silicon nitride having high mechanical strength and excellent heat resistance and boron nitride having excellent thermal shock resistance. It is used as a refractory for continuous casting.

[0003] Here, the above-mentioned conventional method for producing a composite of silicon nitride and boron nitride is based on a method in which a mixture of silicon nitride powder and boron nitride powder is mixed with an oxide of a rare earth element or an oxide such as Al ₂ O ₃ . A method is employed in which a sintering aid is added and mixed, the mixture is shaped, and then sintered.

[0004]

However, in the composite of silicon nitride and boron nitride obtained by the above-described conventional manufacturing method, it is necessary to compensate for the difficulty in sintering of silicon nitride as a raw material powder. An oxide of the rare earth element added and mixed,
Alternatively, an oxide sintering aid such as Al ₂ O ₃ remains as a glassy or crystalline oxide in a grain boundary phase of a sintered body of silicon nitride and boron nitride as a base material after sintering, Since these oxides have much lower thermal shock resistance than a sintered body of silicon nitride or boron nitride, the resulting composite of silicon nitride and boron nitride also has a sufficient thermal shock resistance. There was a problem of not showing sex.

[0005] The present invention has been made in view of the problems of the composite obtained by the above-mentioned conventional manufacturing method, and an object of the present invention is to obtain a composite having a sufficient thermal shock resistance. It is another object of the present invention to provide a method for producing a composite of silicon nitride and boron nitride.

[0006]

As a result of various tests and studies, the present inventors have found that β sialon powder and aluminum nitride powder are used as sintering aids to be added and mixed in order to supplement the sinterability of silicon nitride. Further, the present inventors have found that the thermal shock resistance of the composite of silicon nitride and boron nitride formed when the oxide powder of a rare earth element is used is greatly improved, and completed the present invention.

That is, according to the present invention, a silicon nitride powder and a boron nitride powder are mixed at a weight ratio of 90:10 to 70:30.
In the mixture obtained, the internal ratio to the total amount with the mixture, β
10-30% by weight of sialon powder , 1-6% by weight of aluminum nitride powder , and oxide powder of rare earth element
1-8% by weight of each was added and mixed as a sintering aid,
The present invention provides a method for producing a composite of silicon nitride and boron nitride, which is formed and then sintered.

According to the method for producing a composite of silicon nitride and boron nitride according to the present invention described above, the resultant composite of silicon nitride and boron nitride has significantly improved thermal shock resistance.

This is because, of the sintering aids added and mixed,
The oxygen in the β-sialon powder is stabilized as β-sialon crystals after sintering, and the oxide powder of the rare earth element reacts with silicon nitride as a base material and aluminum nitride powder added as a sintering aid, after sintering, the general formula: M _X (S
i, Al) ₁₂ (O, N) ₁₆ (where M is a rare earth element, X
≦ 2), which is considered to be stabilized as α-sialon crystals, and both of these α-sialon crystals and β-sialon crystals remain in the grain boundary phase of the sintered body in the conventional method. Compared to crystal or oxide glass, its thermal shock resistance is excellent, and as a result, the thermal shock resistance of the resulting composite of silicon nitride and boron nitride is
It is thought that it became higher than the conventional one.

Here, as the silicon nitride powder, a commercially available α-type silicon nitride powder is used, and its average particle size is preferably 2 μm or less. Hexagonal boron nitride powder was used as the boron nitride powder, and the mixing ratio of the silicon nitride and the boron nitride was 90: 1 by weight.
The range is 0 to 70:30. This is because if the proportion of boron nitride is smaller than the above range, the composite effect of boron nitride, that is, the effect of improving the thermal shock resistance of the obtained composite is small,
Further, when the proportion of boron nitride is larger than the above range, the mechanical strength of the obtained composite becomes low.

The β-sialon powder to be added as the sintering aid has a general formula: Si _{6 -Z} Al _z O _Z N _8-Z (Z
≦ 4.2), which may be produced by any method, for example, SiO ₂ —Al ₂
Β-sialon powder obtained by a reductive nitridation method in which carbon powder is added to and mixed with an O ₃ -based raw material and calcined in a nitrogen stream is exemplified.

Further, as the above-mentioned aluminum nitride powder, a commercially available powder is used, and as the rare earth element oxide powder, Y ₂ O ₃ , Yb ₂ O ₃ , Nd ₂ O
₃ , Er ₂ O ₃ or the like can be used. The raw materials to be added and mixed as these sintering aids, that is, the above β-sialon powder, aluminum nitride powder and rare earth element oxide powder have an average particle size of 5 μm or less from the viewpoint of uniform mixing and sintering efficiency. Is preferred.

The amount of each of the above-mentioned sintering aids is 10 to 30% by weight of β-sialon powder and 1 to 6% of aluminum nitride powder in an internal ratio to the total amount of silicon nitride and boron nitride. wt%, and oxide powder of rare earth element Ru is added in an amount of 1-8% by weight. This is because, for any of the components, if the addition amount is smaller than the above range , the subsequent sintering of the mixture becomes insufficient, and the mechanical strength of the resulting composite of silicon nitride and boron nitride is low. In addition, when the amount of addition is larger than the above range , the thermal shock resistance of the composite becomes poor.

The raw material powder described above, silicon nitride,
Mixing of boron nitride, and β sialon powder, aluminum nitride powder and oxide powder of rare earth element which are sintering aids,
Each of the steps of molding and sintering can be performed by conventional means. For example, each component of silicon nitride, boron nitride, and a sintering aid is mixed by a pot mill or the like, and then pressed into a desired shape. And 1650 to 1 in a nitrogen atmosphere.
By sintering at 900 ° C., a composite of silicon nitride and boron nitride having excellent thermal shock resistance can be manufactured.

[0015]

The present invention will be described below in detail with reference to examples.

First, powder of β-sialon used as a sintering aid was synthesized. Synthesis method, SiO ₂ fine powder, aluminum isopropoxide, and Si of the carbon black, Al, and the atomic ratio of C is 1: 0.9: to become 3 are blended, dissolved in isopropyl alcohol Mixed. The mixture was hydrolyzed by adding water, dried, and heated at 1500 ° C. for 6 hours in a nitrogen atmosphere. Thereafter, oxidation treatment was performed in air at 700 ° C. for 5 hours to remove residual carbon. The obtained powder was measured by chemical analysis and X-ray diffraction.
It was confirmed that the powder was a β-sialon powder having a composition of i ₃ Al ₃ O ₃ N ₅ . And the average particle size was 0.7 μm.

Next, α-type silicon nitride powder (Si ₃ N ₄ ) having an average particle diameter of 0.8 μm, hexagonal boron nitride powder (BN) having an average particle diameter of 8 μm, and aluminum nitride powder having an average particle diameter of 1.5 μm (AlN), Y ₂ O ₃ powder having an average particle size of 1.5 μm as an oxide powder of a rare earth element, or an average particle size of 2 μm
m, Yb ₂ O ₃ powder, β-sialon powder synthesized above,
Alternatively, Al ₂ O ₃ powders having an average particle size of 0.8 μm were blended in the proportions shown in Table 1, mixed with a pot mill using methanol as a dispersion medium, and then dried to obtain a raw material for sintering.

The obtained raw material for sintering is formed into a molded body having a width of 50 mm, a length of 50 mm, and a thickness of 7 mm by press molding, and then is sintered under normal pressure at 1780 ° C. for 3 hours in a nitrogen atmosphere. The sintered body is specified in JIS R 1601 “Method for testing bending strength of fine ceramics”.
The test piece was processed.

First, at room temperature, 3
The point bending strength was measured, and this value was used as the reference strength of each test piece. Subsequently, the test piece was placed in an electric furnace maintained at a predetermined temperature, held for 10 minutes, dropped into ice water, and subjected to a thermal shock to measure the three-point bending strength.
The temperature (ΔT value) obtained by subtracting the ice water temperature from the in-furnace temperature which was reduced to half of the reference strength was evaluated as thermal shock resistance. Table 1 shows the results.

[0020]

[Table 1]

From Table 1, it can be seen that test pieces 1 to 8 obtained by the method for producing a composite of silicon nitride and boron nitride according to the present invention.
Is smaller than the test piece 9 obtained by the conventional manufacturing method,
It turns out that the thermal shock resistance is improved.

The mixing ratio of silicon nitride and boron nitride is as follows:
The amount of each of the test pieces 10, 11 or the sintering aid blended at a weight ratio out of the range of 90:10 to 70:30 is determined based on the total amount of silicon nitride and boron nitride. In terms of the ratio, the test piece 12 to which the β sialon powder was added in a range of 10 to 30% by weight, the aluminum nitride powder in the range of 1 to 6% by weight, and the rare earth oxide powder in the range of 1 to 8% by weight were added. In No. 16, it is found that either the thermal shock resistance or the bending strength is deteriorated.

[0023]

According to the above-described method for producing a composite of silicon nitride and boron nitride according to the present invention, the thermal shock resistance is greatly improved without lowering the mechanical strength of the obtained composite. And the industrial application field of the composite material can be expanded.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 35/583-35/596

Claims (1)

(57) [Claims] 1. A weight ratio of silicon nitride powder to boron nitride powder.
To a mixture mixed at a ratio of 90:10 to 70:30 ,
Β Sialon powder in internal ratio to the total amount with the mixture
10 to 30% by weight , aluminum nitride powder 1 to 6 layers
%, And 1 to 8% by weight of the rare earth oxide powder.
A method for producing a composite of silicon nitride and boron nitride, comprising adding and mixing sintering aids in respective proportions, forming the mixture, and sintering the mixture.